Nothing conveys the excitement of space exploration like pictures from another planet. Now NASA is planning to go one better than pictures. The space agency is aiming to launch a probe carrying a communication system that will let future missions to Mars transmit live, high definition video to Earth.

So when the first person walks on Mars, the live video should be far better than what the world saw when Neil Armstrong stepped onto the moon.

As the name suggests, the system used laser light to transmit a video from the moon to Earth in real time.

Using light to transmit information at high speeds is nothing new. You might have fiber optic cables carrying the Internet to your house. But in space, light doesn't travel by cable. A laser is used to send the light signals.

Sending a signal from the moon is one thing. Sending one from Mars is much harder.

"The biggest challenges, by far, have to do with distance," says Kevin Kelly, CEO of LGS Innovations in Herndon, Va., just outside Washington, D.C. The moon is only about 240,000 miles from Earth. Mars is on average 140 million miles away.

From Mars, Earth appears as a small dot. "Keeping [a laser] pointed in the right direction and receiving a strong signal is going to be a physics challenge for sure," Kelly says.

There's one curious problem when pointing a laser from such a great distance. Even travelling at the speed of light, a laser beam can take as long as 20 minutes to go from the Earth to Mars.

"You may receive the signal from the Earth, but you can't just point back at the direction that you got the signal from," says David Israel, principal investigator on NASA's Laser Communications Relay Demonstration mission.

Because by the time your transmission gets to where the Earth is, the Earth has moved out of the beam. You have to point it to where the Earth is going to be when the light signal arrives. This "point ahead" system is like throwing a pass to a receiver in football. If the receiver is running down the field, the quarterback has to throw it to where the receiver is going to be when the ball gets there.

One of the challenges of deep space laser communications is capturing all the light that's sent. To do that, NASA will be using the historic 200-inch Hale telescope on Mt. Palomar in California. The captured light will go into a detector that's being built at NASA's Jet Propulsion Laboratory in Pasadena.

The detectors can measure a single photon of light. "With these detectors we can detect these very faint signals that are going to coming back from this laser transmitter," says JPL physicist Matt Shaw.

NASA's not just interested in using laser communication from deep space. Laser systems can transmit much more data than a radio signal, so they could replace traditional radios on spacecraft.

At MIT's Lincoln Laboratory, engineers are building a miniature system they're planning to send into low Earth orbit space next year.

"The data rates that we're aiming for this demonstration are 200 gigabits per second, 200 billion bits per second," says Bryan Robinson, associate group leader of the optical communications technology group at the lab.

And with a laser in low Earth orbit, you don't need a big telescope to capture the photons. "Between 4 to 8 inches," he says, "maybe as large as a foot. In other words, about the size of a hobbyist's telescope."

Using light to transmit data and video may be the future of space communications, but it's actually quite an old idea. Alexander Graham Bell, the inventor who brought us the telephone, built something called the photophone in the 1880s that transmitted sound using light from the sun.

"Bell demonstrated it right here in Washington, D.C., between a laboratory that was on the roof of a school just near the White House over to his laboratory that was just a few blocks away," says LGS Innovations' Kelly.

Talk about an inventor ahead of his time.

NASA plans to launch its new deep space laser communication system in 2022.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

SARAH MCCAMMON, HOST:

Stephen Hawking was passionate about human exploration beyond our own planet. Now NASA is working on better ways for future missions to send back what they see. It's aiming to test out technology which could allow live, high-definition video to be transmitted from Mars to Earth using lasers. NPR's Joe Palca has this story.

JOE PALCA, BYLINE: All spacecraft have carried some kind of radio to send signals to Earth. The farther you get from Earth, the weaker the signal. For example, this is the best NASA could do with radio in 1969 when Neil Armstrong stepped on the moon.

(SOUNDBITE OF ARCHIVED RECORDING)

NEIL ARMSTRONG: That's one small step for man, one giant leap for mankind.

PALCA: But here's what a broadcast from the moon can sound like now.

(SOUNDBITE OF ARCHIVED RECORDING)

CHARLES BOLDEN: Hello, this is NASA Administrator Charlie Bolden.

PALCA: Bolden wasn't actually on the moon. Instead, a video he recorded was beamed up to the moon and back to Earth in real time. The signal wasn't sent by radio. It was sent using light.

(SOUNDBITE OF ARCHIVED RECORDING)

BOLDEN: This lunar laser communications demonstration is the first time we've used this revolutionary new system to transmit video to and from the moon.

PALCA: Using light to transmit information at high speeds is nothing new. You might have fiber optic cables carrying the Internet to your house. But in space, a laser is used to send the light signals. In this case, a NASA spacecraft pointed a laser beam at a telescope back on Earth and was able to transmit huge amounts of data, enough for a live, high-definition video. And NASA doesn't want to stop at the moon. It's got its sights on Mars.

KEVIN KELLY: I think the biggest challenges by far have to do with distance.

PALCA: Kevin Kelly is CEO of LGS Innovations just outside Washington, D.C., a company that's building part of the laser system NASA is planning to put on a mission out past Mars. Kelly says the moon is only about 240,000 miles from Earth, Mars is about 140 million. And from Mars, Earth appears as a small dot.

KELLY: Keeping this thing pointed in the right direction and receiving a strong signal is going to be a physics challenge for sure.

PALCA: One curious problem - you can't actually point the laser at Earth. You have to point it where the Earth is going to be when the light signal arrives. This point-ahead system is like throwing a pass to where a receiver is going to be in football. Now, laser light is made up of photons, and because the laser NASA is planning to use is not all that powerful, you need to capture every last photon you can from the satellite out in space. That's where Matt Shaw's work comes in. Shaw's lab is in the basement of a building at the Jet Propulsion Laboratory in Pasadena. He opens a plastic box to show me what looks like gold computer chips.

MATT SHAW: So these are the largest single photon detectors of this kind that have been made.

PALCA: That squeaking sound in the background is part of a special refrigeration system. These chips have to be cooled to almost absolute zero in order to work.

SHAW: With these detectors, we can detect these very faint signals that are going to be coming back from this laser transmitter.

PALCA: Using light to transmit data and video may be the future of space communications, but it's actually quite an old idea. Kevin Kelly says the same inventor who brought us the telephone built something called the photophone in the 1980s that transmitted sound using light from the sun.

KELLY: Alexander Graham Bell demonstrated it right here in Washington, D.C., between a laboratory that was on the roof of a school just near the White House over to his laboratory that was just a few blocks away.

PALCA: Talk about an inventor ahead of his time. NASA plans to launch its new deep space laser communication system in 2022. Joe Palca, NPR News.